study guide gi physiology Flashcards
list the four basic layers of the gastrointestinal tract? from inside out?
muscosa
submucosa
muscularis
serosa
what is the innermost layer of the gi tract
mucosa
what are some of the functions of the mucosa
secretion of mucus and digestive enzymes and hormones
absorptions of nutrients
and protection against infectious disease
what is the predominant tissue type that is found in the mucosa?
simple columnar epithelial cells which are found on a thin layer of connective tissue containing capillaries which nourish the cells and allow for absorption.
what is the two functions of the submucosa?
1) enables the gastrointestinal tract to regain its shape after food moves through it.
2) houses an intrinsic neuronal system called the enteric nervous system which regulates digestive activities such as motility, secretion, and blood flow.
what is the predominant tissue type found in the submucosa?
elastic fibers
what is the function of the muscularis?
sphincters (valves)
coordinated contractions of the muscularis layer are responsible for peristalsis and other contractions (segmentation) that propel food forward.
what is the predominant cell types found in the muscularis?
circular and longitudinal layered smooth muscle
what is the function of the serosa?
protective outermost layer of the GI tract, supports structures
secrete serous fluid that lubricates the organs reducing friction during movement
the intestine also receives extrinsic innervation from the?
autonomic nervous system
what neurons regulate rest and digest?
parasympathetic
parasympathetic cholinergic neurons release what?
acetylcholine
acetylcholine does what?
increases secretions and contractions of the intestinal smooth muscle
the sympathetic neurons release what? which do what?
epinephrine and norepinephrine
drive the fight or flight response
what is the effect the sympathetic noradrenergic activity have on the gi system?
decreases the activity of intestinal smooth muscle, reduces secretions, and causes sphincters to contract, thus blocking the progression of intestinal contents.
how many nerve fibers from the enteric nervous system are there?
approximately 100 million
the majority of the ENS nerve fibers are found distributed where?
within the walls of the gastrointestinal tissues
the enteric nervous system is primarily localized to two extensive plexuses which are?
myenteric plexus and the submucosal plexus
a plexus is what?
a collection of nerves
the plexuses of the ENS are primarily found where?
the inner tissue layers of the GI tract
where is the myenteric plexus located?
between the longitudinal and circular muscle layers of the GI tract
the myenteric plexus is primarily responsible for?
control of muscular contraction and the mechanical aspect of digestion
where is the submucosal plexus located?
in the submucosa
what is the function of the submuscosal plexus of the ENS?
responsible for controlling digestive secretions, absorption, and local contraction of the submucosal muscle leading to enfolding of the mucosa.
what do the efferent nerve fibers of the ENS do?
carry signals into the ENS from the ANS
what does the afferent nerve fibers of the ENS do?
carry signal from the alimentary canal to the ENS triggering peristalsis and secretions.
what allows for higher level control of digestion?
some afferent nerve fibers run into the vagus nerve and back to the brain stem allowing for higher level control of digestion
where do afferent nerve fibers originate?
in wall of gut
neurotransmitters control the gastrointestinal activity are both _______ and ________.
inhibitory and excitatory
List some examples of how neurotransmitters control GI activity
affect secretions into the lumen of the gut
control muscular contractions and gut motility
overactivity or under-activity of any neurotransmitter and ENS pathways can lead to?
excessive or diminished secretions
excessive or diminished absorptions
excessive motility
prolonged residents of food and chyme in various components of the GI tract
what sensation may you feel if the ENS is functioning abnormally?
pain and other sensations
the esophagus recieves food mixed with? from where?
saliva
mouth
relaxation of the __________- allows food to enter the upper portion of the esophagus.
upper esophageal sphincter
what propels the food to the lower esophageal sphincter?
esophageal contractions
the lower esophageal sphincter is ________ active. meaning what?
tonically active
it is in a contracted state
the LES does what to allow food to enter the stomach?
relaxes reflexively
the LES remains closed between what to prevent regurgitation of gastric contents into the esophagus?
swallowing
name the three different muscles found in the esophagus?
smooth muscle in the muscularis layer of the esophagus
skeletal muscle
smooth muscle fibers
skeletal muscle in the esophagus is from the?
diaphragm
smooth muscle fibers in the esophagus are from the?
stomach
describe a burp?
occasionally the LES will open after a meal to expel swallowed air
what is the temporary storage unit where chemical digestion of food begins?
stomach
ingested contents and digestive secretions are mixed by coordinated muscular contractions forming a semi solid paste called?
chyme
chyme is made of what two things?
ingested contents and digestive secretions
the stomach is divided into three major regions called the?
cardia
fundus
antrum
the lining of the stomach is covered with a _______ epithelial cells folded into gastric pits.
columnar
each gastric pit is an opening of a duct into which one or more what empty?
gastric glands
what is also known as the corpus of the stomach?
fundus
the glands in the stomach house four type of secretory cells which are?
mucus cells
parietal cells
chief cells
endocrine cells
what is the function of mucous cells?
mucus secreiton
parietal cells primary cell function?
gastric acid secretion
chief cells primary cell function?
pepsinogen and lipase secretion
what is endocrine cells also called?
g cells
what is endocrine cells primary cell function?
gastrin secretion
where does most chemical digestion occur?
body and fundus of the stomach
under normal conditions how much gastric juice is released from the gastric mucosa throughout the day?
3 liter
gastric juice consists of?
electrolytes
hydrocholirc acid
mucus
intrinsic factor
the primary secretion of the stomach is what produced by the parietal cells.
hydrogen ions
what two mechanisms control gastric secretions?
neural and hormonal
what three things stimulate parietal cells to secrete hydrogen ions?
acetylcholine
gastrin
histamine
what can directly stimulate the proton potassium ATPase pump and parietal cells.
gastrin
gastrin can stimulate what to secrete histamine?
Enterochromaffin ECL
What inhibits acid secretion (2 things)
somatostatin and prostaglandins (specifically PGE 2)
what type of cells produce gastrin?
g cells a type of endocrine cell that resides in the gastric glands of the gastric antrum
chyme is passed from stomach to the duodenum by passing through the?
pyloric sphincter
where is the primary site for mixing of chyme?
small intestine
the small intestin is the primary site for mixing chyme with additional secretion from what two areas to promote digestion and reabsorption?
common bile duct and pancreatic duct
the main method of the small intestine for increasing digestion and absorption is by?
providing large surface area to do so
name 4 ways the small intestine has a large surface area?
length is 5 meters
mini folds of mucosa and submucosa allow for greater surface area
mucosal layer intestinal wall have finger like projection (villi) increasing absorption
epithelial cells have microvilli on the apical surface which helps to increase surface area
the mucosa and submucosa’s villi and microvilli increase the absorptive surface area of the small intestine by how much?
600 fold
how many layers of epithelial cells between the intestinal lumen and the systemic blood? and they shed how often?
1
every 2-6 days
what two things will attach to receptors and causing influx of calcium in the regulation of gastric secretion?
acetylecholine and gastrin
the colon consist of three parts which are?
duodenum
jejunum
ilium
what is the primary function of the small intestines?
digestion/absorption of ingested nutrients (carbs, proteins, lipids)
gastrin released by g cells stimulate ECL to release what?
histamine
histamine binds to h2 receptors which increases what?
intracellular CAMP
what acts in opposition to histamine to decrease intracellular cAMP
PGE2
what act together to increase activity fo ATPase in the regulation of gastric secretion?
Calcium and cAMP
the stomach is exposed to gastric juice with a pH of?
1.5 to 3.5
the acidic environment aids in what? and destroys what?
aids in digestion and absorption of ingested contents
destroyes ingested bacteria and microorganisms
the stomach is protected fromt he acidic environment by what?
by coating itself with mucosal barrier consisting of bicarbonate rich mucus
the mucosal barrier strongly adheres to the epithelials cells of the stomach of the mucosa and protects it by maintain a thin layer of pH that is approximately?
6 to 7
the stomachs underlying tissue between the epithelial cells and mucosa is protected from the acidic environment by what?
tight junctions preventing gastric juic from leaking into the underlying tissue
smooth muscle cells in the walls of the GI tract are packed together in __________ and _________ bundles.
circular and longitudinal bundles
what functionally couple the smooth muscle cells of the gi tract so contraction occurs synchronously.
gap junctions
what is receptive relaxation?
as ingested food travels down the esophagus, the stomach reflexively relaxes to allow food to enter
the stomach can accommodate about ____ liters of food?
1.5 liters
what two things increase the frequency and magnitude of stomach contractions, augmenting gastric mixing.
gastrin and acetylcholine
the gastric contents are mixed completely and converted to semi solid state called chyme usually within ___ hours after a meal is ingested.
4 hours
in order for chyme to enter the small intestine the pyloric sphincter acts as a filter, allowing only _____ amount of chyme to pass through.
3 milliliters or less
the rate of gastric emptying depens on what?
the chemical and physical contents of the stomach
carbohydrate meals empty slow or fast?
fast
fatty meals form a_______ at the top fo the chyme and move through the stomach _______.
oily layer
slowly
dietary carbohydrates are most commonly composed of _______ and ______.
polysaccharides and disaccharides
enterocytes can only absorb?
monosaccharides
give an example of a polysaccharide?
starch
give an example of a disaccharide
sucrose and lactose
carbohydrate digestion occurs in _______ stages
two
along the brush border of the intestinal lumen starch
